The present invention relates to an abrasive article comprising a plurality of abrasive composites or agglomerates, methods of making the abrasive article, and methods of using the abrasive article to abrade workpiece surfaces. More specifically, the abrasive article includes porosity dispersed throughout the abrasive article among the plurality of abrasive composites or agglomerates.
Glass articles are found extensively in homes, offices, and factories in the form of lenses, prisms, mirrors, CRT screens, and other items. Many of these glass surfaces are used with optical components which require that the surface be optically clear and have no visible defects and/or imperfections; such a surface finish is often referred to as a mirror finish. If present in or on the surface, defects, imperfections, and even minute scratches may inhibit the optical clarity of the glass article. In some instances, these defects, imperfections, and/or minute scratches may inhibit the ability to accurately see through the glass. Glass surfaces used with optical components, for example, must be essentially free of any defect, imperfection, and/or scratch.
Articles made from other materials, such as metals, plastics, and ceramics, are also found extensively in homes, offices, and factories. Similar to glass articles, these articles often need to have a mirror finish, that is, a surface that is essentially free of any defect, imperfection, and/or scratch. Examples of articles that need a very fine surface finish include magnetic recording items such as hard disk substrates and electronic components such as read-write heads in computers.
Abrasive finishing processes have been widely used to remove imperfections and/or defects such as mold lines, rough surfaces, small point and other small imperfections in glass and other workpieces. The abrasive finishing typically falls within three main processes: grinding, fining, and polishing.
Grinding steps perfect the desired curve or radius and remove any casting defects by rough grinding the glass surface with an abrasive tool. Typically this abrasive tool contains superabrasive particles such as a diamond, tungsten carbide, or cubic boron nitride. However, the abrasive tool in this rough grinding process will impart coarse scratches to the glass or other surface such that resulting surface is neither precise enough nor smooth enough to directly polish to an optically clear state or other desired finish. The objective of the grinding process is to remove large amounts of material quickly and fairly accurately while leaving as fine of a scratch pattern as feasible. These scratches are then typically removed by further steps commonly known as xe2x80x9cfiningxe2x80x9d and xe2x80x9cpolishingxe2x80x9d.
Glass fining and polishing is typically done with a loose abrasive slurry which comprises a plurality of abrasive particles dispersed in a liquid medium such as water. Ceramic and many other articles are also polished with a loose abrasive slurry. The most common abrasive particles used for loose slurries are pumice, silicon carbide, aluminum oxide, and the like. The loose abrasive slurry may optionally contain other additives such as dispersants, lubricants, defoamers, and the like. In most instances, the loose abrasive slurry is pumped between the surface that is being finished and a lap pad, such that the loose abrasive slurry is present between the surface and the lap pad. Typically, the workpiece and the lap pad will move relative to each other while maintaining contact. This process typically comprises one or more steps, with each step generating a progressively finer surface finish on the workpiece surface.
What usually is desired is an abrasive article that effectively and economically grinds a surface in a short time period by providing fast stock removal while introducing minimal surface and subsurface damage and scratching.
The present disclosure is directed to an abrasive article for polishing, finishing, or otherwise providing a desired finish on a workpieces, such as on hard drive media or disks. Unlike conventional abrasive articles which have a tendency to chip and scratch workpieces that are hard and/or brittle, the abrasive articles of the present disclosure provide a fine and scratch-free surface with minimal surface damage. The construction of the abrasive article is particularly useful with abrasive particles having an average particle dimension of about 10 micrometers and less, and is especially useful with abrasive particles having an average particle dimension of about 6 micrometers and less. In some embodiments, the abrasive article is useful with abrasive particles having an average particle dimension of about 3 micrometers and less.
The abrasive article is formed from a plurality of abrasive composites or agglomerates bonded together in a material to create an abrasive article. Each composite has a plurality of primary abrasive particles bonded by a first binder matrix; the primary abrasive particles can be individual abrasive particles or aggregates of abrasive particles. When viewed from the perspective of the overall abrasive article, the abrasive composites act as abrasive particles; when viewed from the perspective of the abrasive composites, each abrasive composite is an abrasive tool or article, and the primary abrasive particles are individual abrasive particles.
The abrasive article is a three-dimensional abrasive article, having a thickness that is greater than the thickness of one abrasive composite. The abrasive article has a thickness that is greater than the thickness of at least 1 abrasive composite, preferably at least 5 abrasive composites, and more preferably is greater than the thickness of at least 10 abrasive composites.
In one embodiment, an abrasive article, such as a grinding wheel, is provided by bonding primary, abrasive particles with an inorganic first binder matrix to form abrasive composites. These abrasive composites, in turn, are bonded together to form the abrasive article.
The abrasive article includes (1) pores disposed within the abrasive composites and (2) between and among the abrasive composites; these porosities are referred to as xe2x80x9cintra-compositexe2x80x9d porosity and xe2x80x9cinter-compositexe2x80x9d porosity respectively. Typical levels of intra-composite porosity are about 5 to 60 volume percent, although in some embodiments, it may be desired to minimize the intra-composite porosity; that is, it can be desired to have the intra-composite porosity approaching zero percent. As a consequence of the composite formation process, some level of intra-composite porosity is typically present; it may be desired to introduce additional porosity in some embodiments. Inter-composite porosity is between and among the abrasive composites. Typical levels of inter-composite porosity are about 25 to 75 volume percent. Of this porosity, the ratio of the two porosities, that is, the ratio of the intra-composite to the inter-composite porosity, can range from about 1:2 to 2:1, or can vary from this. Typically, the level of intra-composite porosity will differ from the level of inter-composite porosity.
The combination of inter- and intra-composite porosity allows the use of much smaller primary abrasive particles than have been useful in related articles of the art. These articles combine an unusually high cut rate with a fine surface finish.
The abrasive composites are formed with an organic or inorganic first binder matrix bonding the primary abrasive particles together. The composites can be regularly shaped or irregularly shaped. Examples of inorganic first binder matrixes include metals, ceramics, glasses, and oxides. Preferably, an inorganic first binder matrix, such as a ceramic matrix or a glass matrix, is used. In one particular embodiment, primary abrasive particles, such as diamond particles, having an average particle dimension of about 0.1 to 1 micrometer, are formed into regularly shaped, cube-like abrasive composites having an average dimension of about 90 micrometers.
These abrasive composites are then bonded, for example, with a second binder material, to form an abrasive article having about 20 to 65% porosity. That is, about 20 to 65% of the volume of the abrasive article is free of both second binder material and abrasive composites. The second binder material is an inorganic material, such as a ceramic or a glass. In one embodiment, the abrasive composites are bonded to form an abrasive article having about 20 to 55% porosity. This porosity may be distributed throughout the abrasive article as any combination of intra-composite and inter-composite porosity. In some embodiments, the second binder material may be present at a level higher than a preferred level; this may be preferred when the second binder material is a relatively soft, or erodible material.
The abrasive article can be a unitary article, such as grinding wheel or stone, or can be composed of multiple segments of bonded abrasive composites.